This invention relates to improved oscillators for producing an output signal oscillating at a frequency varying in correspondence with changes in the level of an input voltage signal.
Copending U.S. patent application Ser. No. 902,687 filed May 4, 1978 by Bernard R. Zuvela et al on "Remote Well Signalling Apparatus and Methods" discloses a well signalling system in which information is conveyed upwardly from deep within a well to the surface of the earth by frequency modulated signal currents transmitted through the earth formation surrounding the well. The oscillating signal currents in the earth desirably vary in frequency within a rather narrow range, and may be produced by a voltage controlled oscillator in which the frequency and period of the output signal vary in correspondence with changes in the input voltage level. In order to assure proper interpretation of the frequency modulated signals at the surface, the voltage controlled oscillator must be very precise and reliable in its regulation of the output frequency, and preferably is essentially linear in response.